Microelectronic package having direct contact heat spreader and method of manufacturing same

ABSTRACT

A method of fabricating a microelectronic package having a direct contact heat spreader, a package formed according to the method, a die-heat spreader combination formed according to the method, and a system incorporating the package. The method comprises metallizing a backside of a microelectronic die to form a heat spreader body directly contacting and fixed to the backside of the die thus yielding a die-heat spreader combination. The package includes the die-heat spreader combination and a substrate bonded to the die.

FIELD

Embodiments of the present invention relate generally to packagingmicroelectronic dice to produce integrated circuits. It particularlyrelates to packaging a microelectronic die for greater heat dissipation.

BACKGROUND

Processors and related computer components are becoming more powerfulwith increasing capabilities, resulting in increasing amounts of heatdissipated from these components. Similarly, package and die sizes ofthe components are decreasing or remaining the same, which increases theamount of heat energy given off by the component for a given unit ofsurface area. Furthermore, as computer-related equipment becomes morepowerful, more chips are mounted to the printed circuit board, and moreand more components are being placed inside the equipment or chassiswhich is also decreasing in size, resulting in additional heatgeneration in a smaller volume of space. Increased temperatures canpotentially damage the components of the equipment, or reduce thelifetime of the individual components and equipment. In addition, somecomponents are more susceptible to damage resulting from stress andstrain occurring during testing, packaging, and use.

One prior art method of bonding a microelectronic die to a heat spreaderincludes a packaging technology that places one or more thinned dice ona planar heat spreader and secures the dice on to the heat spreaderusing a bonding process involving an adhesive material, such as solder,or a polymeric material, or, in the alternative, using a directmetallurgical bond, such as may be formed by an interdiffusion of Au(gold) and Si (silicon). Where a metallurgical bond is to be establishedas noted above, such a prior art process however requires a heating ofthe die/heat spreader assembly in order to form the bond.

Disadvantageously, however, heating to create the bond as noted abovemay involve temperatures from about 150 to about 300 degrees Celsius,and may as a result create unwanted stresses and cracking involving thedie, the heat spreader and/or the bonding material (or thermal interfacematerial, hereinafter “TIM”) therebetween during a cool down phase ofthe bonding process. In addition, unwanted stresses on the die candisadvantageously have a negative impact on the performance of circuitcomponents on the die. Moreover, where gold is used as part of thesolder bonding of the die to the heat spreader, a cost of the package isdisadvantageously increased. Furthermore, since the prior art involvesthe use of a TIM to establish a bonding of the die to the heat spreader,thermal resistance of the TIM can disadvantageously negatively impact aperformance of circuit components of the die.

The prior art fails to provide a reliable, simple and cost-effectivetechnique of providing a microelectronic die exhibiting improved heatdissipation characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are illustrated by way of example and notby way of limitation in the figures of the accompanying drawings, inwhich the like references indicate similar elements and in which:

FIG. 1 is a schematic representation of a microelectronic die to be usedin a package according to embodiments;

FIGS. 2, 3 a and 3 b are a schematic representations showing the die ofFIG. 1 as having been bonded to a double-sided substrate according to anembodiment;

FIG. 4 is a schematic representation of an encapsulant as having beenprovided between a landside of the substrate of FIG. 3 a and an activesurface of surface mount components bonded to the substrate according toan embodiment;

FIG. 5 is a schematic representation showing a protective mask as havingbeen provided to protect the substrate and the surface mount componentsduring metallization according to an embodiment;

FIGS. 6 a and 6 b are schematic representations showing a metallizationprocess according to an embodiment;

FIG. 7 is a schematic representation of a microelectronic package formedaccording to an embodiment;

FIG. 8 is a schematic representation of a microelectronic die to be usedin a package according to embodiments;

FIGS. 9 a and 9 b are schematic representations showing a metallizationprocess according to an alternate embodiment;

FIG. 10 is a schematic representation of a microelectronic packageformed according to an alternate embodiment;

FIG. 11 is schematic representation showing a secondary heat spreader ashaving been attached to the heat spreader body of the package of FIG. 7;

FIG. 12 is a schematic representation of an alternate embodiment of aheat spreader body;

FIGS. 13 a-13 c are schematic representations showing a metallizationprocess according to yet another embodiment; and

FIG. 14 is a schematic representation of a system incorporating apackage according to an embodiment.

DETAILED DESCRIPTION

A method of fabricating a microelectronic package having a directcontact heat spreader, a package formed according to the method, adie-heat spreader combination formed according to the method, and asystem incorporating the package are described herein.

Various aspects of the illustrative embodiments will be described usingterms commonly employed by those skilled in the art to convey thesubstance of their work to others skilled in the art. However, it willbe apparent to those skilled in the art that the present invention maybe practiced with only some of the described aspects. For purposes ofexplanation, specific numbers, materials and configurations are setforth in order to provide a thorough understanding of the illustrativeembodiments. However, it will be apparent to one skilled in the art thatthe present invention may be practiced without the specific details. Inother instances, well-known features are omitted or simplified in ordernot to obscure the illustrative embodiments.

The phrase “one embodiment” is used repeatedly. The phrase generallydoes not refer to the same embodiment, however, it may. The terms“comprising”, “having” and “including” are synonymous, unless thecontext dictates otherwise.

Referring now to FIG. 1 by way of example, embodiments of the presentinvention comprise providing a microelectronic die, such as die 110shown in FIG. 1. As shown, die 110 has an active surface 114 and abackside 112 as shown, and includes electrical contacts (not shown) atthe active surface thereof for electrical and mechanical bonding to asubstrate, as would be recognized by one skilled in the art. Optionally,according to an embodiment, the die may be a thinned die, such as die110 shown in FIG. 1. In other words, optionally, the thickness of thedie may be decreased, for example to about 100 microns or less, by oneor more of various techniques known in the art, such as plasma etching,chemical etching, grinding, or polishing. Advantages of providing athinned die include a reduction in a thermal resistance of a combinationof the die with a heat spreader and a resultant improvement in theextraction of heat from the die; an improved compliance of the die toexpansions and contractions of the heat spreader and a resultantreduction in stress-induced failures in the solder joints and of thedie.

As seen in FIGS. 2, 3 a and 3 b by way of example, an embodiment of thepresent invention comprises bonding the die to a microelectronicsubstrate. By “bonding,” what is meant in the context of the presentinvention is a mechanical and electrical joining between electricalcontacts on the active surface of the die and lands on the die-sidesurface of the substrate. Bonding could include, as would be recognizedby one skilled in the art, any of the well known flip-chip packagingprocesses. Thus, bonding could include, as suggested by way of examplein FIG. 2, a selective coating of the lands on the substrate with solderdeposits, a registration of the electrical contacts on the activesurface of the die with the lands, and a soldering, such as a reflowing,of the contacts on the active surface of the die with the lands on thedie-side of the substrate to solidify the solder deposits to formsolidified solder joints, and an optional provision of encapsulantand/or underfill material about the solidified solder joints. Thus, FIG.2 shows die 110 as having been bonded to a die side 116 ofmicroelectronic substrate 118 by way of solidified solder joints 120. Asalso shown in the figures, optionally, according to an embodiment, themicroelectronic substrate is a double-sided substrate, and includessurface mount components such as capacitors at a landside thereofopposite the die side thereof. Thus, substrate 118 as shown isdouble-sided and includes surface mount components 122 at a landside 124thereof opposite the die side 116 thereof.

Referring next to FIGS. 3 a and 3 b by way of example, as noted above,bonding could further include, as would be recognized by one skilled inthe art, the provision of an encapsulant, such as encapsulant 126 and/orthe provision of underfill material, such as underfill material 125(FIG. 3 b), to fill the gap between the die and the substrate, such asgap 128 shown in FIG. 2. As is well known, encapsulant and/or anunderfill material is typically used in order to compensate fordifferences in coefficients of thermal expansion (CTE's) between thesubstrate and the die. As shown in FIGS. 3 a and 3 b, encapsulant, suchas encapsulant 126 may be flush with a backside 112 of die 110. Thereare a number of ways to provide the encapsulant, as would be recognizedby one skilled in the art. According to one well known method, as shownin FIG. 3 a, a mold (not shown) in the shape of the encapsulant to beprovided may be placed about the die and the substrate such that a moldcavity thereof encompasses the gap, and the gap within the mold may befilled with a molded encapsulant material that is flowed into the moldcavity in liquid form and is then solidified in the mold to yieldencapsulant 126. In the alternative, as shown in FIG. 3 b, a capillaryunderfill material 125 may be provided in the gap, such as gap 128,using a dispenser. Thereafter a mold may be placed about the die and thesubstrate as noted above, and a molded encapsulant material 126 thenflowed into the mold cavity and cured within the mold to yield theencapsulant. An example of the molding material (i.e. an encapsulantmaterial) may include PLASKON MUF-2A manufactured by the CooksonElectronics Co., Alpharetta, Ga., USA. Optionally still, should thereremain any molding material on the backside of the die, planarizationaccording to any one of well known methods, such as, for example,chemical mechanical polishing or grinding, may be applied to the diebackside in order to make the encapsulant flush with the same.

It is noted that, while FIGS. 2, 3 a and 3 b show stages in a flip chipbonding process which involves a sequential soldering and provision ofencapsulant and/or underfill material, embodiments further includewithin their scope a bonding process where both the soldering and theprovision of an encapsulant and/or underfill material occur at the sametime, such as, for example, a TCB NUF process (or thermo-compressionbonding and no-flow underfill process), or any other of the well knownflip chip bonding processes, as would be within the knowledge of oneskilled in the art.

As next seen in FIG. 4 by way of example, where the substrate is adouble-sided substrate, and further where surface mount components areconnected to a landside of the substrate, an embodiment of the presentinvention comprises providing encapsulant to fill the gaps between thesurface mount components and the landside of the substrate, such asencapsulant 130 to fill gaps 132 as shown in FIG. 4. According to anembodiment, the encapsulant, such as encapsulant 130, may be providedaccording to any one of the methods known to persons skilled in the art,such as, for example, those outlined with respect to encapsulant 126above.

Referring next to FIG. 5 by way of example, an embodiment of the presentinvention comprises providing a protective mask on a landside of thesubstrate and on a backside of any surface mount components on thelandside of the substrate to protect the landside of the substrate andthe backside of surface mount components from a metallization process ofa backside of the die Thus, as suggested in FIG. 5, an embodimentcomprises providing a protective mask 134 onto the landside 124 ofsubstrate 118 and onto the backside of surface mount components 122 asshown. The mask may include a tape, such as, for example, 3M™ CircuitPlating Tape 1279 or INT 600 Masking Tape, manufactured by theIntertronics Company, Oxfordshire, ENGLAND, and may be applied usinglamination, in order to protect the landside of the die from asubsequent metallization of the die backside. In the alternative, themask could be a soft rubber pad with recessed cavities to accommodatethe surface mount components on the landside of the substrate. When thesubstrate is pushed against the rubber pad under a pressure which couldbe provided by a fixture, the rubber pad will seal and protect thesubstrate landside. Where there are no surface mount components on thelandside of the substrate (not shown), the mask may be applied accordingto an embodiment to cover the entire landside of the substrate. Inaddition, according to an embodiment, where surface mount components maybe present on the die side of the substrate (not shown), a mask wouldalso be provided on the die side of the substrate, as would berecognized by one skilled in the art.

As next seen in FIGS. 6 a and 6 b by way of example, embodiments of thepresent invention comprise metallizing a backside of the die to form aheat spreader body directly contacting and fixed to a backside of thedie (that is, a “direct contact heat spreader” according toembodiments). By “heat spreader body,” what is meant in the context ofthe present description is a heat spreader including a body made of ahighly thermally conductive material to extract heat away from a die,such material including, by way of example, metals such as copper,copper alloys including copper alloys with tungsten, copper laminates,copper composites containing particles having a thermal conductivityabove that of copper (i.e. above about 400 W/m/K, such as, for example,diamond), aluminum, aluminum alloys, and the like. By “directlycontacting,” what is meant in the context of the present description isa contact which is not established by way of a layer intermediate to thedie and the heat spreader, such as, for example, by way of a thermalinterface material, including, for instance, thermal grease, epoxy,solder, thermally conductive adhesive, or any other of the well knownthermal interface materials according to one skilled in the art.According to an embodiment, the heat spreader body may have a thicknessof about 0.2 mm to about 3 mm. While FIGS. 6 a and 6 b showmetallization stages of the backside 112 of die 110 which involveselectroplating according to a preferred embodiment to form the heatspreader body directly contacting the backside of the die, metallizationof the backside of the die according to embodiments is not so limited,and may be performed according to any one of other well known methods,such as, for example, electroplating or electroless plating, sputtering,chemical vapor deposition, and evaporation.

Thus, referring now to the embodiment of FIG. 6 a, metallization may beaccomplished by first providing a conductive seed layer 140 onto thebackside 112 of die 110 as shown, and thereafter, as shown in theembodiment of FIG. 6 b, by providing a electrolytically plated metallayer 142 onto the seed layer 140 to form the heat spreader body 138.The seed layer according to embodiments may be made of a materialadapted to serve as an electroplating site for a subsequentlyelectrolytically deposited layer. Thus, depending on the material of thelayer to be electrolytically deposited, the material of the seed layermay include, by way of example, copper, nickel, or silver, and may beprovided using electroless plating or sputtering. If either copper,silver, or another noble metal is used as a seed layer, then, anadhesion/barrier layer would additionally be provided such as Ti/TiN,Ta/TaN etc, as would be recognized by one skilled in the art. Such as anadhesion/barrier layer may be deposited by sputtering, ALD or CVDAccording to a preferred embodiment, the seed layer includes a layer ofcopper provided through electroless plating. Referring to FIG. 6 a,provision of the seed layer 140 in the shown embodiment results in apartially masked intermediate package combination 144 including the die110, the substrate 118, the encapsulants 126 and 130, the solder joints120, the surface mount components 122, the seed layer 140 and theprotective mask 136. After provision of the seed layer as shown by wayof example in FIG. 6 a, the partially masked intermediate packagecombination may be submerged into a bath of plating solution containingions of the metal to be electroplated, such as, for example, copper, andan electroplating process may cause the electroplated layer 142 to beformed on the backside of the die. It is noted that, as would berecognized by one skilled in the art, by virtue of the fact that theseed layer 140 serves as a site of atomic nucleation for theelectroplated layer 142, once the layer 142 is provided, seed layer 140would no longer be readily identifiable as such, and is hence no longershown in FIG. 6 b. It is further noted that, while metallization asshown in the embodiment of FIGS. 6 a and 6 b involves a metallization ofa surface of encapsulant 126 flush with the backside of the die,resulting in a heat spreader body 138 that is wider than a width of thedie 110 as shown, embodiments of the present invention encompass withintheir scope the provision of a heat spreader body that has any suitablewidth, including a width that is smaller than or substantially equal toa width of the die (not shown). According to one embodiment, particleshaving a thermal conductivity above that of the metal of the heatspreader body, such as, for example, above that of copper, that is,above about 400 W/m/K, may be dispersed in the plating solution. Aresulting electroplated layer 142 would then contain the particlesentrapped therein after its formation, the particles enhancing a thermalconductivity of layer 142 and hence a thermal performance of the heatspreader body 138. Preferably, the particles have a thermal conductivitybetween about 100 W/m/K and about 5000 W/m/K. More preferably, theparticles are made of diamond.

Thereafter, according to an embodiment, the protective mask may beremoved from the landside of the substrate and from a backside of anysurface mount components on the landside of the substrate to yield amicroelectronic package. Removal of the protective mask may be effectedaccording to any one of well known methods, such as, for example,through peeling.

Referring next to FIG. 7 by way of example, a microelectronic package146 includes a substrate 118 including surface mount components 122 at alandside thereof, a die 110 bonded to the substrate, and a directcontact heat spreader 138 fixed to the backside of the die, that is, adirect contact heat spreader. A microelectronic package formed accordingto embodiments would include at least a die bonded to a substrate andhaving a heat spreader body directly contacting and fixed to a backsideof the die. It is thus not necessary according to embodiments that thesubstrate be double-sided, or that there be one or more surface mountcomponents bonded to the landside of the substrate during metallizationof the die. In the event that no surface mount components are bonded tothe landside of the substrate during metallization, fabrication of amicroelectronic substrate would include all of the sub-processesoutlined above with respect to the embodiment of FIGS. 1-7, except forthe provision of a protective mask on surface mount components (forexample, FIG. 5) where metallization is to involve plating. In thelatter instance, a protective mask would be provided according to anembodiment to cover an entire landside of the substrate beforemetallization. Where surface mount components are to be provided on thelandside of the substrate, they could in turn be provided aftermetallization of the backside of the die according to any one of wellknown methods that could also involve the provision of encapsulant asdescribed above by way of example in FIG. 4.

Referring next to FIGS. 8-9 b by way of example, an embodiment of thepresent invention alternative to that shown for example in FIGS. 1-6 bcomprises providing a microelectronic die, and, before bonding the dieto a substrate, metallizing a backside of the die to form a heatspreader body directly contacting and fixed to a backside of the diethereby yielding a die-heat-spreader combination. The provision of amicroelectronic die according to an embodiment may involve the provisionof a plurality of as yet unsingulated dice on a wafer. Metallization maythen involve metallization of a backside of all dice on the wafer, andthereafter singulation in order to obtain individual die-heat-spreadercombinations. In the alternative, the provision of a microelectronic dieaccording to another embodiment may involve the provision of an alreadysingulated die. After metallization, to form the microelectronic packagesimilar to the package 146 of FIG. 7, for example, the die-heat-spreadercombination may then be bonded to a substrate in any one of well knownmanners, such as, for example, in the manner described above withrespect to FIGS. 2 and 3. Moreover, where the substrate is adouble-sided substrate including surface mount components on a landsidethereof, encapsulant may be provided between the surface mountcomponents and the landside of the substrate in any one of well knownmanners, such as, for example, the manner described above with respectto FIG. 4.

Thus, as seen in FIG. 8, a die 220 may be provided similar to die 110shown in FIG. 1. Thus, die 220 may be either thinned or not thinnedaccording to application needs. Die 220 has an active surface 214 and abackside 212 as shown. Next, as shown in FIGS. 9 a and 9 b by way ofexample, metallization of a backside of the die may be effected asdescribed above in relation to the embodiment of FIGS. 6 a-6 b.

Referring then to FIG. 9 b by way of example, metallization according toan embodiment may result in a die-heat-spreader combination, such asdie-heat-spreader combination 250 as shown, where a heat spreader body242 directly contacts and is fixed to the backside 214 of die 210.Similar to FIGS. 6 a and 6 b, while FIGS. 9 a and 9 b show metallizationstages of the backside 212 of die 210 which involves electroplatingaccording to a preferred embodiment to form a heat spreader body 242,metallization of the backside of the die according to embodiments is notso limited, and, as noted above with respect to FIGS. 6 a and 6 b, maybe performed according to any one of other well known methods, such as,for example, electrolytic plating, sputtering, chemical vapordeposition, and evaporation. Referring now to the embodiment of FIG. 9a, metallization may be accomplished by first providing a conductiveseed layer 240 onto the backside 212 of die 210 as shown, andthereafter, as shown in the embodiment of FIG. 9 b, by providing anelectroplated layer 242 onto the seed layer 240 to form the heatspreader body 238. Similar to FIGS. 6 a and 6 b, according to anembodiment, the heat spreader body may have a thickness of about 0.3 mmto about 3 mm. As noted above, the seed layer according to embodimentsmay be made of a material adapted to serve as an electroplating site fora subsequently electrolytically deposited layer. Thus, depending on thematerial of the layer to be electrolytically deposited, the material ofthe seed layer may include, by way of example, copper, nickel or silver,and may be provided using electroless plating or sputtering. Accordingto a preferred embodiment, the seed layer includes a layer of copperprovided through electroless plating. Referring to FIG. 9 a, provisionof the seed layer 240 in the shown embodiment results in an intermediatecombination 244 including the die 210 and the seed layer 240. Afterprovision of the seed layer as shown by way of example in FIG. 9 a, theintermediate combination may be submerged into a bath of ionic solutioncontaining ions of the metal to be electroplated, such as, for example,copper, and an electroplating process may cause the electroplated layer242 to be formed on the backside of the die 210. It is noted that, byvirtue of the fact that, as is would be recognized by one skilled in theart, the seed layer 240 serves as a site of atomic nucleation for theelectroplated layer 242, once the copper layer 242 is provided, seedlayer 240 would no longer be readily identifiable as such, and is henceno longer shown in FIG. 9 b. Although metallization as noted withrespect to the embodiments of FIGS. 6 a and 6 b show a resultant heatspreader body 138 that is wider than a width of the die 110, in the caseof an embodiment where a backside of the die is metallized before abonding of the die to a substrate, such as is the case with respect toFIGS. 9 a and 9 b, the resultant heat spreader body, such as body 238,may have a width that is generally substantially equal to a width of thedie, such as die 210.

Referring next to FIG. 10 by way of example, embodiments of the presentinvention contemplate bonding the die-heat-spreader combination, such ascombination 250, to a substrate, such as substrate 218, in any one ofwell known manner in order to yield a microelectronic package 246.Similar to package 146 of the embodiment of FIG. 7, package 246 includesa die 210 bonded to a substrate 218 by way of solder joints 220 andencapsulant 226, a heat spreader body 238 having been formed on abackside of die 210 to form a direct contact heat spreader. Surfacemount components 222 are shown as having been provided on the landsideof substrate 218, and encapsulant 230 is provided between the surfacemount components 222 and the landside of substrate 218, although it isunderstood that the present invention is not limited to the provision ofsuch surface mount components, or to a double-sided substrate, aselaborated upon with respect to the embodiment of FIG. 7 above.

Preferably, a heat spreader body is provided according to embodiments toadequately remove heat from the die according to application needs.However, if the heat spreader body is not configured to do so, asecondary heat spreader may be attached to the heat spreader body in anumber of well known manners. Where a protective mask is used, thesecondary heat spreader may be attached either before or after removalof a protective mask as described above in relation to FIG. 6 a,according to application needs. The material used to fabricate thesecondary heat spreader may include, by way of example, metals (such ascopper, aluminum, and alloys thereof), ceramics (such as SiC, and AlN),a heat pipe, or other structures adapted to remove thermal energy. Inthis context, reference is made to FIG. 11. It is noted at the outsetthat although FIG. 11 depicts the provision of a secondary heat spreaderon a package similar to package 146 of the embodiment of FIG. 7, asecondary heat spreader could equally as well have been provided ontothe package 246 of the embodiment of FIG. 10, or onto any other packageconfiguration formed according to embodiments of the present inventionas noted above.

Referring now to FIG. 11 by way of example, according to someembodiments, attaching a secondary heat spreader to the heat spreaderbody includes using a thermal interface material to attach the secondaryheat spreader to the heat spreader body. According to embodiments, whena secondary heat spreader is attached to the heat spreader body using athermal interface material, a thickness of the thermal interfacematerial is usually no larger than about 200 microns, and preferably nolarger than about 50 microns. The TIM may include, for example, a solderincluding, for example, In, Sn, or InAg, and may be provided as solderperform. The TIM may also include polymer based materials, for example,a thermally conductive adhesive including a silver particle filled epoxypaste or a ceramic particle filled epoxy paste.

Referring in particular to FIG. 11 by way of example, an additional heatspreader, such as secondary heat spreader 310, may be attached to theheat spreader body, such as heat spreader body 138, by way of a thermalinterface material (or “TIM”), such as TIM 312. The secondary heatspreader 310 may further be sealed to the substrate 118 via seals 314 asshown. In the case of FIG. 11, where the package is provided asdescribed with respect to FIGS. 1-6 b, it is preferable then for theprotective mask 136, as shown in FIGS. 5, 6 a and 6 b for example, to beremoved before or after sealing of the heat sink 310. If the package isprovided as described with respect to FIGS. 8-9 b (not shown), however,no protective mask would have been needed on the landside of thesubstrate in the first instance, as explained above.

Referring now to FIG. 12 by way of example, an alternative configurationis shown for a package according to an embodiment. FIG. 12 shows apackage 546 similar to package 146 of FIG. 7, except that the heatspreader body 538 is not a continuous structure, but rather includes amicrochannel structure 552 for liquid cooling as shown. Thus, accordingto embodiments, it is not necessary that the heat spreader body be acontinuous body as shown for example in FIGS. 7 and 10. The heatspreader body according to embodiments may have any shape configured todissipate heat from the die. The microchannel structure 552 of FIG. 12may be obtained via a plating of a backside of the die according to anyone of methods well known in the art to obtain the shown structure.Thereafter, a flat cover piece 554 made of a material similar to that ofthe microchannel structure may be attached to the microchannel structureaccording to any one of well known methods in order to closemicrochannels 555 of the microchannel structure 552. For example, thecover piece 554 may be attached to the microchannel structure 252 by wayof soldering. The resulting structure 256 including a heat spreader bodyincluding the microchannel structure 552, to which is attached a coverpiece 254 as seen in FIG. 12. Package 546 of FIG. 12 also includes a die510 bonded to a substrate 518 via solder joints 520 and encapsulant 526,comparable to the configuration of FIG. 7.

Referring then to FIGS. 13 a-13 c by way of example, metallizationaccording to an embodiment may involve plating bonding. Referring now tothe embodiment of FIGS. 13 a and 13 b, metallization may be accomplishedby providing a conductive seed layer 640 onto the backside 612 of die610 as shown, and thereafter, by providing a flat copper piece 651including pedestals 653 at a die side surface thereof onto the seedlayer 640. Seeding of the die backside 612 may be accomplished accordingto any one of the well known methods, such as those described above, forexample, with respect to FIG. 6 a. Thereafter, as shown in theembodiment of FIG. 13 c, a gap 655 between a die side of the copperpiece 651 and the backside 612 of the die 610 created by the pedestals653 is electroplated to yield an electroplated layer 642 onto the seedlayer 640 to form the heat spreader body 638. Similar to FIGS. 6 a and 6b, according to an embodiment, the heat spreader body may have athickness of about 0.3 mm to about 3 mm. The resultant structure is amicroelectronic package 646 as shown in FIG. 13 c, including a substrate618, onto which a die 610 is bonded via solidified solder joints 620 andencapsulant 626, a direct contact heat spreader or heat spreader body638 having been provided on the backside of the die according to anembodiment. Advantageously, plating bonding reduces the metallizationtime with respect to regular plating methods, and thus provides anefficient and cost-effective manner of metallizing the die backside.

An advantageous aspect of a microelectronic package formed according toan embodiment is that, because a provision of the heat spreader bodyonto the backside of the die occurs at room temperature, a residualstress in the silicon of the substrate is less than or equal to about 50MPa at room temperature, as opposed to comparable packages of the priorart, where high temperature processing creates much higher residualstresses in the silicon. In addition, at least where plating is used tometallized a backside of the die, a grain boundary and grain orientationof the metal of the heat spreader body at a region of the heat spreaderbody adjacent the backside of the die may be distinguished with respectto a grain boundary and grain orientation of the metal of the heatspreader body at other regions thereof.

Advantageously, embodiments of the present invention provide a method offabricating a microelectronic package including a direct contact heatspreader which allows direct contact between the die and the heatspreader for improved heat dissipation capacity when compared withpackages of the prior art. Moreover, a method according to embodimentsallows the provision of a heat spreader onto the backside of a die atroom temperature, thus advantageously reducing stresses on the dieproduced by a high temperature bonding of the heat spreader to accordingto the prior art, reducing reliability risks in the die silicon, andminimizing an impact on the performance of circuit components presentwithin the die. Additionally, embodiments allow a cost effective way ofproviding a heat spreader on the backside of a die by obviating a needfor the use of gold, such as used in some packages of the prior art tobond a heat spreader to the die. Moreover, the provision of a directcontact heat spreader according to embodiments, by improving thermalperformance, advantageously either obviates the use of the TIM betweenthe die and heat spreader body or, in the alternative, provides for theprovision of an additional secondary heat spreader onto the heatspreader body by way of TIM that is typically at least about 50% thinnerthan TIM's of the prior art. A thinness of a TIM is used according to anembodiment of the present invention is brought about by virtue of thefact that there would be substantially no CTE mismatch between thesecondary heat spreader and the direct contact heat spreader.

Referring to FIG. 14, there is illustrated one of many possible systemsin which embodiments of the present invention may be used. The shownsystem 90 therefore comprises a microelectronic assembly 1000 whichincludes a package such as, for example, package 146 of FIG. 7 orpackage 246 of FIG. 10 described above. In an alternate embodiment, theelectronic assembly 1000 may include an application specific IC (ASIC).Integrated circuits found in chipsets (e.g., graphics, sound, andcontrol chipsets) may also be packaged in accordance with embodiments ofthis invention.

For the embodiment depicted by FIG. 14, the system 90 may also include amain memory 1002, a graphics processor 1004, a mass storage device 1006,and/or an input/output module 1008 coupled to each other by way of a bus1010, as shown. Examples of the memory 1002 include but are not limitedto static random access memory (SRAM) and dynamic random access memory(DRAM). Examples of the mass storage device 106 include but are notlimited to a hard disk drive, a compact disk drive (CD), a digitalversatile disk drive (DVD), and so forth. Examples of the input/outputmodule 1008 include but are not limited to a keyboard, cursor controlarrangements, a display, a network interface, and so forth. Examples ofthe bus 1010 include but are not limited to a peripheral controlinterface (PCI) bus, and Industry Standard Architecture (ISA) bus, andso forth. In various embodiments, the system 90 may be a wireless mobilephone, a personal digital assistant, a pocket PC, a tablet PC, anotebook PC, a desktop computer, a set-top box, a media-center PC, a DVDplayer, and a server.

Although specific embodiments have been illustrated and described hereinfor purposes of description of the preferred embodiment, it will beappreciated by those of ordinary skill in the art that a wide variety ofalternate and/or equivalent implementations calculated to achieve thesame purposes may be substituted for the specific embodiment shown anddescribed without departing from the scope of the present invention.Those with skill in the art will readily appreciate that the presentinvention may be implemented in a very wide variety of embodiments. Thisapplication is intended to cover any adaptations or variations of theembodiments discussed herein. Therefore, it is manifestly intended thatthis invention be limited only by the claims and the equivalentsthereof.

What is claimed is:
 1. A microelectronic package comprising: asubstrate; a die having an active surface and a backside and beingbonded to the substrate at the active surface thereof; an encapsulantsurrounding the die and substantially planar with the backside of thedie; a heat spreader body directly contacting and fixed to the backsideof the die wherein the heat spreader body including one of a barrierlayer and a seed layer in direct contact with the backside of the dieand the encapsulant surrounding the die.
 2. The package of claim 1,wherein the die comprises silicon and wherein a residual stress withinthe silicon at room temperature is below about 50 MPa.
 3. The package ofclaim 1, wherein a grain boundary and grain orientation of a metal ofthe heat spreader body at a region of the heat spreader body adjacentthe backside of the die is different from a grain boundary and grainorientation of the metal of the heat spreader body at other regions ofthe heat spreader body.
 4. The package of claim 1, further comprisingsolder joints and at least one of an encapsulant and an underfillmaterial disposed between the active surface of the die and a die-sideof the substrate to bond the die to the substrate.
 5. The package ofclaim 1, wherein the heat spreader body is made of a material comprisingat least one of copper, a copper alloy, a copper laminate, a coppercomposite, aluminum and an aluminum alloy.
 6. The package of claim 1,wherein the heat spreader body comprises a metal composite materialcomprising a metal and particles having a thermal conductivity abovethat of the metal.
 7. The package of claim 1, wherein the heat spreaderbody includes a microchannel structure, the package further comprising acover piece attached onto the microchannel structure.
 8. The package ofclaim 2, further comprising a heat sink attached onto the heat spreaderbody with a thermal interface material.
 9. The microelectronic packageof claim 1 wherein said heat spreader body has a thickness between about0.2 mm and about 3 mm.
 10. The microelectronic package of claim 1wherein said heat spreader body has a width larger than a width of saiddie.
 11. A die-heat spreader combination comprising: a die having anactive surface and a backside; an encapsulant surrounding the die andsubstantially planar with the backside of the die; and a heat spreaderbody directly contacting and fixed to the backside of the die whereinthe heat spreader body comprises a material selected from the groupconsisting of copper, a copper alloy, a copper laminate, a coppercomposite, aluminum and an aluminum alloy and wherein the heat spreaderbody including one of a barrier layer and a seed layer in direct contactwith the backside of the die and the encapsulant surrounding the die.12. The die-heat spreader combination of claim 11, wherein the heatspreader body includes a microchannel structure.
 13. The die heatspreader combination of claim 11 wherein said heat spreader body has awidth larger than a width of said die.
 14. A system comprising: amicroelectronic assembly including: a microelectronic packagecomprising: a substrate; a die having an active surface and a backsideand being bonded to the substrate at the active surface thereof; anencapsulant surrounding the die and substantially planar with thebackside of the die; a heat spreader body directly contacting and fixedto the backside of the die wherein said heat spreader body has athickness greater than about 0.2 mm and wherein the heat spreader bodyincluding one of a barrier layer and a seed layer in direct contact withthe backside of the die and the encapsulant surrounding the die; and amain memory coupled to the microelectronic assembly.
 15. The system ofclaim 14, wherein the heat spreader body is made of a materialcomprising at least one of copper, a copper alloy, a copper laminate, acopper composite, aluminum and an aluminum alloy.
 16. The system ofclaim 14 wherein said heat spreader body has a thickness between about0.2 mm and about 3 mm.
 17. The die heat spreader combination of claim 11wherein said heat spreader body has a thickness greater than about 0.2mm.
 18. The die heat spreader combination of claim 11 wherein said heatspreader body has a thickness between about 0.2 mm and about 3 mm. 19.The system of claim 14 wherein said heat spreader body has a widthlarger than a width of said die.